1. Field of the Invention
The present invention relates to an apparatus and method for sanitizing a filter system, and to methods for improving the quality of filtered water.
2. Description of the Related Art
Filtration systems are widely used in many industries, including, for example, municipal water systems, industrial water systems, the beverage industry, and in pharmaceutical production. These systems are used to improve the quality of a fluid, particularly water, by removing undesirable contaminants such as pathogenic micro-organisms, suspended solids, particulate matter, and dissolved chemicals. Dissolved and suspended chemical contaminants may enter the supply through a number of pathways including pollution, natural processes, and sanitization processes. The concentration levels of these chemicals may be limited by regulation or by end user requirements.
Filtration systems generally utilize a filter media to separate substances from a fluid. Particulate bed, or particle bed filtration systems, involve using particulate matter as the filter media. Particulate beds allow a fluid to pass through the bed while retaining suspended solids and substances dissolved in the fluid. As material accumulates on the surface of the filtration media and in the interstices of the particulate bed, the efficiency of the bed decreases, evidenced by a decrease in filtrate flow and an increased pressure drop across the bed. To return the system to a more efficient state, the bed may be replaced, but it is often more economical to clean the filtration media.
One method of cleaning the filtration media is by backwashing. This procedure involves temporarily reversing the flow of fluid through the filtration media to dislodge contaminants that have accumulated in or that have adsorbed onto the bed. The backwash fluid may be filtered or supply water and, in some instances, detergents or other additives may be added to aid in dislodging contaminants. Generally, the backwash fluid is discharged to waste. In some industries, it is common for some filters, e.g. carbon tower filters, to be backwashed on a regular basis.
Backwashing is often useful in removing the bulk of any micro-organisms from the filtration system, but it does not sanitize the system. In addition, backwashing may introduce some previously retained micro-organisms into the filtrate. As a result, filtration systems may also require regular sanitization of the bed or other parts of the system. For instance, at least weekly sanitization of carbon tower filtration systems is often recommended in the beverage industry.
Sanitization may be achieved through a variety of processes and agents including, for example, chlorine or steam. Such procedures are generally lengthy and require careful monitoring. Typically, the filtration system is out of service while it is being sanitized, and the sanitizing agent often must be purged from the system before the system can be brought back on line.
Municipal water treatment stations typically introduce free chlorine through the use of chlorine gas according to the following reactions:
Cl2+H2O←xe2x86x92HOCl+H+Clxe2x88x92xe2x80x83xe2x80x83(1)
HOCl←xe2x86x92H++OClxe2x88x92xe2x80x83xe2x80x83(2)
Chlorine is an effective sanitization agent for municipal water supplies, but free chlorine tends to react with organic compounds in water systems to produce, for example, tri-halo-methanes. The speciation of free chlorine is pH dependent. Therefore, free chlorine can exist as either hypochlorous acid (HOCl) or hypochlorite ion (OClxe2x88x92) depending on the pH. Hypochlorous acid is much more effective in the destruction of bacteria than is the hypochlorite ion.
Chloramines are also frequently used as sanitizing agents and are more stable in water than conventional chlorine. xe2x80x9cChloramine,xe2x80x9d as used herein, is a generic term describing the various reaction products of ammonia and chlorine. Chloramines may undesirably affect the characteristics of the product water and any process equipment in contact with the water, such as, for example, reverse osmosis membranes. Therefore, many industrial users, such as producers of pharmaceuticals and beverages, would like to be able to remove sanitizing agents such as chloramines before using the water produced from the filtration system in production processes. Like free chlorine, the speciation of chloramines is pH dependent, with monochloramine predominating at about neutral pH. Chloramines are known to be difficult to remove from water, and industry professionals have struggled with various ways to treat filter beds, particularly GAC, to provide for their more efficient removal. One way that chloramines are currently removed involves adsorbing the chloramines onto carbon. Carbon, however, has a low affinity for the predominant form of chloramine, monochloramine. Moreover, GAC beds require frequent replacement, and may promote the growth of micro-organisms in the system.
Because unwanted chemicals and micro-organisms may be present anywhere in a filter system, it may be desirable to sanitize and cleanse the entire system and not just the particulate bed. In such instances, steam is generally used, which is more thorough than chemicals and backwashing. Steam that is forced through a system will contact many parts of the system. Therefore, steam is capable of sanitizing and cleaning the exposed components of filter systems, not just the filter media. However, as steam condenses, the condensate may accumulate in pockets that are known as xe2x80x9cdead spots.xe2x80x9d Thus, pockets of contaminated condensate and associated contaminants may remain in the system, free to re-contaminate the filter bed.
All conventional methods of sanitizing a filtration system suffer from inefficiencies and/or limited effectiveness. Conventional backwashing and sanitization generally require large amounts of water and require that the system be off-line for significant periods of time. Moreover, typical chemical sanitization agents are generally expensive and may be toxic. The use of steam to sanitize a system requires significant amounts of energy, which may be expensive, and the process may not be totally effective. Therefore, it has been difficult to maintain a contaminant- and pathogen-free filter system while minimizing water use and system downtime.
Accordingly, a need exists for improved methods and apparatus for sanitization and cleaning of filtration systems.
Accordingly, in one embodiment, the present invention is directed to a method for sanitizing a filtration apparatus. The method includes providing a filtration apparatus having an inlet at a first end, an outlet at a second end, and a filtration media positioned between the outlet and the inlet. A fluid at a temperature of at least 160xc2x0 F. is allowed to flow through the apparatus in a direction opposite that of normal operational flow for a period of time sufficient to reduce the viability of any micro-organisms contained in the apparatus. In one aspect, the method involves fluidizing a particulate bed while allowing the fluid to flow through the apparatus. In another aspect, the method involves adjusting the pH of the fluid.
Another embodiment of the invention is directed to an apparatus for sanitizing a filtration system. The apparatus includes an inlet that is in fluid communication with a pump and may be coupled to a filtration system. The pump is in fluid communication with a heat exchanger and with an outlet that may be configured to be coupled to the filtration system. The system may also include an inductor and may be a mobile unit.
In another embodiment, the invention is directed to a filtration system. The filtration system includes a chamber in fluid communication with a first port and second port, the first port including a conduit fluidly connected to the chamber. A filter is positioned in the chamber, and a scavenger is positioned in the conduit. The scavenger provides fluid communication between the chamber and the conduit at a bottom portion of the chamber.
Another embodiment of the invention is directed to a method for providing a substantially chloramine-free aqueous filtrate. The method involves reducing the pH of an aqueous fluid by, for example, adding carbon dioxide. The reduced pH aqueous fluid is then filtered through a filter bed, providing a filtrate that contains lesser quantities of chloramine. Specifically, the method may be used to convert a portion of the monochloramine contained in an aqueous fluid to dichloramine, the latter having a higher affinity for the granular activated carbon (GAC) that may comprise the filter bed. Such a method is capable of extending the useful life of the filter bed.